Iron-nickel-titanium alloy



Patented July 21, 1936 UNITED STATES IRON-NICKEL-TITANIUM ALLOY Norman B. Pilling, Elizabeth, and Paul Dyer Merica, Plainfield, N. J., assignors to The International Nickel Company, Inc., New York, N. Y., a corporation of Delaware No Drawing. Application April 15, 1929, Serial No. 356.870

Claims.

This invention relates to improved alloys of the solid solution type containing nickel, and more particularly to so-called austenltic steels containing nickel and the development of high strength properties in such alloys.

Hitherto it has been proposed to utilize the metal titanium as a deomdizing agent for alloy steelsand the like in which the residual content of titanium contemplated was very small, usually less than .1 percent. It has been further proposed to use titanium as a toughening agent or grain refiner in which cases the alloy may have some 1 percent of titanium retained, although several disclosures specify ranges of titanium for such purposes up to 10 percent. It is an object of the present invention to provide improved hardenable nickel alloys by combining with a suitable alloy, referred to as the base alloy. quantities of titanium and titanium-like elements.

It is a further object of this invention to confer hardening properties upon particular base alloy compositions chosen to provide other desirable properties, whereby not only the hardness but-"the elastic strength and breaking strength of the base alloy is increased without materially changing its other characteristic properties.

It is a still further object of this invention to alloy a suitable hardening agent with a nickelbearing base material and subject the resulting alloy to a particular heat treatment to develop and control increased strength properties. These and other desirable advantages of the present invention will be set forth and described in the accompanying specification, certain preferred compositions being given by way of example only, for, since the underlying principles may be applied to other specific compositions, it is not intended to be limited to those herein shown except as such limitations are clearly imposed by the appended claims.

The present invention comprehends a wide variety of base alloy compositions and three preferred hardening agents, as will be described more in detail hereinafter. The preferred base alloy which is particularly amenable to the proposed treatment may be defined as nickel-bearing solid solutions having the face-centered cubic behave substantially similarly, and which behavior will be described more in detail below. No exceptions to this definition have yet been encountered, although the degree of hardening displayed by difierent combinations of base alloy and hardening agent, of course, vary somewhat in degree. In one such series, viz., ironnickel-chromium-titanium, the hardening characteristics were displayed in alloys having ranges of nickel content varying from substantially 6 to 96 percent.

The preferred hardening agents comprehended within the spirit and scope of this invention are titanium, aluminum, and zirconium, and it is apparent that the hardening characteristics herein disclosed may be properties or functions of the boron and the titanium groups of the periodic classification of the elements according to Mendeleif. Of these hardening agents titanium has been found to be the more useful from the standpoint of developing physical properties of engineering value combined with practical working qualities.

For purposes of illustration, in order to more clearly set forth the novel features of the present invention, the characteristics of iron-nickel base alloys alloyed with titanium as a hardening agent will be discussed. Nickel-iron alloys which include from about 25 percent to substantially 100 percent nickel in their composition are soft and relatively unaifected in hardness by heat treatment. Titanium is soluble in these alloys and, if completely dissolved therein, the resulting ternary alloys retain substantially the original soft character. If a suflicient amount of titanium be added, however, the resulting alloys are soft only when cooled rather rapidly from a high temperature; if reheated to some lower temperature range, or allowed to cool rather slowly through this range, a substantial rise in hardness occurs. A still further increase in titanium content causes the alloys to become increasingly hard, even when subjected to rapid cooling from high temperatures, yet these alloys change somewhat in hardness with heat treatment. These characteristics in a series of iron-nickel alloys containing 35 percent nickel and varying amounts of titanium are shown in the following table:

Number 1 2 3 4 5 6 7 Percent titanium o .49 1. s1 2. 2o 3. 1a 4. 00 s. 71 B me No 1ooo 0., air cool 132 131 131 151 118 268 393 r 100 0., 3 hrs. water quenched.- 132 138 197 307 327 311 380 lattice type of crystalline structure. The claim,

for this broad definition is predicated on experimental work with six distinct alloy seriesof this type in addition to the metal nickel, all of which The desirable range of titanium to be added to this particular base is from substantially 1 percent, at which point hardening begins, to about 4 percent, at which point the malleability of the alloys becomes impaired. The hardened alloys in common with iron-nickel alloys generally are characterized by their toughness, resistance to attack by non-oxidiring acids, term-magnetism. and high electrical resistivity. With an increase in the nickel content of the base alloy, the desirable range of titanium, as just defined, remains substantially the same up to '75 percent nickel content, but the capacity for hardening displayed by the alloys under consideration, steadily diminishes with increase in nickel content up to 99% with a range of about 150 to 225 Brinell hardness units. Within the range of to 96 percent nickel content, the minimum titanium content necessary to develop hardening, increases from about 1 percent to somewhat more than 4 percent, the amount being roughly proportional to the excess, of nickel over 75 percent. Within this range the hardness difierential developed by heat treatment is from about 75 to substantially Brinell units. Titanium when added to many other nickel alloys of the face centered cubic lattice type previously noted, permits the formation of alloys having hardening characteristics similar to the ironnickel-titanium alloys described. Among these other base alloys may be mentioned: Iron-nickelcopper; iron-nickel chromium; iron-nickel-manganese; nickel-copper; nickel-chromium, and nickel metal. The following table shows several malleable alloys exemplifying this fact, the hardness numbers being expressed in Brinell units:

and/or zirconium for the titanium. In the following table a few typical. alloys are given by way of example. i

Number 1s 19 2o 21 4 Fe 55 as cs 62 Ni 38.7 33.6 17.4 34.0 Cu 5.9 Or 8.2 .41 5.1 4.4 5.4 Zr 2.0

Brinell hardness Soit coco 0. water number quench) 154 172 157 Hard (600 0. temp.) 21s 2st 282 183 In the case of aluminum, the content of this element necessary to develop suitable hardening response varies from about 2.5 to substantially 6 percent, the latter percentage marking the approximate upper limit of forgeability. A preferred range is from 5.0 to 5.5 percent.

When titanium is used as an alloying element, the use of commercial ferro-titanium may introduce appreciable quantities of aluminum and silicon into the metal, both of which elements will appear in the resulting alloy. This content of aluminum is not harmful and it has now been found in fact that the use of even higher contents of aluminum in combination with titanium as hardening agents ofiers certain advantages, notably in accelerating the rate at which the Number 8 9 10 11 12 13 14 16 17 Ni 63. 4 43 30 35 23. 3 18. 4 l5. 3 35. 5 93 80 Fe 3. 1 35 53 61 65 66 57 1. 2 9 Cu 27. 2 19 8. 0 1. 1

C 7. 9 11. 8 14. 5 8. 0 Mn 5. 1

So (10(X) 0. water quench) 130 127 157 159 154 153 152 126 104 Hard (tempered 600700' C.) Z37 271 302 3 5 315 304 284 266 317 The ranges of the several elements in addition to titanium may be extended as follows: copper .5-40%, chromium 3-30%, nickel 2-99%. and iron 2-90%, the titanium being replaceable, under the conditions discussed more in detail hereinafter, by from .5-10% of titanium-like metals such as aluminum and/or zirconium. These elements may be associated with each other in any desired amounts to give compositions having certain specified characteristics.

The preferred range of titanium is substantially from 1 to 4 percent. This range is determined approximately by the first appearance of hardening and the substantial disappearance of hot malleability. When it is desired to retain good hot and cold working properties in order to permit shaping by forging, hot rolling, cold rolling, drawing, or plastic deformation generally, full advantage cannot be taken of the maximum titanium content. In such cases it is preferable to employ titanium contents ranging from 2.2 to 3.2 percent for alloys having a low carbon content and in which the base is nickel-iron, nickel-copper-iron,

and nickel-chromium-iron. It will, of course, be

understood that in case of castings where work- .ability is not a factor to be considered, a. much 0 greater range of titanium is permitted with a corhardening reaction occurs. As an example of this discovery, the nickel-iron-titanium alloy including 34.8 percent nickel, 2.2 percent titanium, and 0.3 percent aluminum, showed no appreciable hardening when air-cooled from 1000 degrees centigrade. A similar alloy including 34 percent nickel, 2.5 percent titanium, and 1.9 percent aluminum increased in hardness about 110 Brinell units on air-cooling. Both alloys hardened to about 320 Brinell units when furnace cooled. It will also be appreciated that by the use of hardening agents in multiple as herein described, it is possible to secure marked economies in manufacture due to the ability to use'cheaper.

addition materials without in any way sacrificing the good results desired in the finished product.

The diversity of base compositions amenable to hardening by titanium and aluminum has been described. No common alloying elementsin amounts less than 2 percenthave been found to interfere with this hardening characteristic with the exception of aluminum and carbon. The effect of aluminum when combined with titanium has just been described. Since carbon forms an inert titanium carbide, its presence with titanium is highlydetrimentah This is due to the fact that although the total titanium content may be great enough to indicate vigorous hardening, the alloy is, in fact, devoid of hardening response. It is highly desirable, therefore, to keep the carbon content as low as is metallurgically feasible.

Alloys of thisv type havebeen produced with as little as .01 percent carbon, yet melts containing as much as 0.40 percent carbon have been produced which displayed good hardening properties, although an inefliciently high titanium content ultimately developed. Since the rate of hardening diminishes as the temperature is decreased. an optimum hardening temperature may be appropriately designated.

in the alloy was necessary. With a hardening treatment which includes It is considered to be within the scope of this holding the alloy at a fixed temperature for sevinvention to P v n dd to h maj eral hours, the preferred hardening temperaelements-of compo iti n, such other elements as ture is substantially 700 degrees C. for alloys in used in metallurgy to fi in which titanium is the hardening element, and mung purifymg' djegasifymgi and otherwlse treat about 600 degrees C. when aluminum or zirconiigfi g m g ig g gi gg ggg g g 2:32; um is the hardening element. It is to be noted ry that when chromium does not exceed about 5 Percent percent, good hardening may be produced by fur- Manganese up to 5 izacc cooling from the softening range. When Silicon up to5 the chromium content exceeds this value, the Aluminum up to 1 hardcning reaction proceeds sluggishly, and con- Vanadium upto 1 siderably more time is required in order to dezi m up t 1 velop'full hardness. High chromium alloys con- Titanium up to taining up to 30% chromium may show very little Calcium up to hardening on furnace cooling. Magnesium up to A; When it is desired to develop the maximum Boron up to /2 hardness of a given alloy, it has been found ad- The nature and quantity of these accessory vantageous to carry out the hardening operaelements is determined by the nature of the base hens in several steps at progressively lower temalloy in question. peratures and preferably with the duration of To bring the alloys under consideration into heating increasing at he lower temperaturesthe softest working condition, the heat treatment The temper e range in which this incremental required in all cases is a not too slow cooling from hardening may be carried out is from the miniabove a minimum temperature. Most efiicient 1 mum softening temperature above described, results a t d when t s i u down to about 500 degrees c. As a particular experature is exceeded, but the temperature margin ample, an alloy of a composition including by which it is exceeded is not of very great importance, the upper limit usually being that at Ni 221 which an undesirable coarsening in grainsize 63 occurs. The minimum softening temperature Ti varies directly with increase in content of the Fe B841 hardening element or elements, and also varies to some extent with the composition of the base alloy. For contents of titanium and/or aluminum having g g i Brmfeu hardnessfof 1 hardwhich yield malleable alloys, this minimum ened to Brmen a ter twenty our ours of temperature is generally from 750 degrees centitreatment at 7 degrees when mere grade to 850 degrees centigrade, and can easily be mental hardemng heat treatment was gwen to established for a particular alloy. Asa general this alloy, a hardness of 340 Brmen units was rule entire group of alloys herein described Cured, the particular treatment illcluded respond well to a range of softening temperaat 750 degrees C. for two hours, followed by heat tures varying from 900 degrees C. to 1050 degrees treatment at 680 degrees'cfor five hours, and

C. The rate of cooling required to avoid hardat 600 degrees for tye oursening is not great, and air cooling will usually AS exemplifying physical P DGIt ES Dro- -prove fast enough, although cooling in water or duced in malleable alloys f t ype U der sonin oil is permissible. sideration, the following table is included:

No. Ni Cu Cr Ti Fe Temper E515? s rgi i 'th gegog 't 3,11%? 151%.

22 at as as as a, a silt 3%:283 33:3 23:?

Soft 24,000 88,000 48 0s 24 15.5 12.4 2.7 Ba]. {Hard(a) 00,000 130,000 30 62 Hard(b) 80,000 100,000 22 1s (a) 700 0. Temp. (b) Incremental temper.

Whereit is desired to heat treat the alloys in In addition to exhibiting these high physical order toharden them, the treatment is much properties at room temperatures, the high more variable. Variations in composition of the strength and elastic properties shown may be r base metal, and of the hardening elements affect tained at high temperatures, provided that the both the temperature at whichthe desired hardbase alloy is of a suitable type; iron-nickel-chroening is most effectively produced, and also the mium is appropriate, and the titanium alloy rate at which it occurs. In all cases hardening with this base shows excellent strength properoccurs over a considerable range of temperatures, ties at temperatures up to the hardening tempera and the lower the temperature at which this can ture. The steel designated as number 24' in the be carried out, the greater will be the hardness above table shows the following characteristics when broken in tension at 600 degrees C.-atter to cause titanium to go into solution, quenching previous full hardening:

90,000 psi PL. 125,000 psi ULT. 25% Elong. in 2" 12% Red. area Such alloys are particularly suited for purposes like apparatus which may be used in oil-crack-.

ing and oil refining.

Many alloys, in particular steels, exist which have hardness and tensile properties equal to or even excelling the alloys of the present type. The advantage of the latter lies in the unique fact that the present hardening elements may add hardening properties to. particular base alloys without detriment to their other distinctive properties, thus afiording a combination of strength with other special qualities not previously possible. For example the addition of titanium to austenitic nickel-chromium steels imparts hardness and high elastic properties without interfering with the valuable corrosion. and heat resisting qualities of the latter. In particular cases in which a property is closely associated witha specific nickel content, e. g., low expansivity in nickel-iron alloys, a slight adjustment of composition may be necessary in the hardened alloy. This adjustment generally involves a small increase in nickel content.

It will now be appreciated that there has been provided an improved process for producing high strength alloys of the solid solution type containing nickel, which are initially soft and workable, which process comprehends the use of suitable amounts of hardening agents such astitanium, aluminum and/or zirconium. It is to be noted further that the hardenable alloys comprehended within the spirit and scope of the present invention, are adapted for a wide variety of uses, and more particularly for use in structures which can economically be made by plastic deformation such as drawing, pressing, etc., such formed articles being adapted to being suitablyhardened by a heat treatment as set forth.

It will be observed that the present invention provides a thermally hardened article-of manufacture of a nickel alloy in which the hardening agent, such as titanium, aluminum or the like is incorporated in an amount which is in excess of its solid solubility and which is suflicient to make the nickel alloy thermally hardenable and softenable. I

What is claimed is:

1. A hard nickel-iron alloy containing abou 2% to about 50% nickel, more than 1 to about 10% titanium, andiron constituting substantially the balance of the alloy, said alloy being age hardened by heating the alloy to an elevated temperature below its melting point but sufliciently high to cause titaniumto go into solution, quenching the alloy and reheating to a temperature below that of the initial heating but sufliciently high and for a period of time sumcient-to obtain a substantial increase in the hardness of the alloy.

2. A hard nickel-iron alloy containing about 2% to about'50% nickel, more than 1 to about 4% titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating the alloy to an elevated temperaetween 750 C. and themelting point to dissolve the alloy and reheating to a temperature below that of the initial heating but sufliciently high and for a period of time sumcient to obtain a substantial increase in the hardness of the alloy. 5

3. A hard nickel-iron alloy containing about 2% to about 50% nickel, about 2.2% to about 3.2% titanium, and ironconstituting substantially the balance of the alloy, said alloy being age hardened by heating the alloy to an elevated 10 temperaturebelow its melting point but sufliciently high to cause titanium to go into solution, quenching the alloy and reheating to a temperature below that of the initial heating but sumciently high and for a period of time suilicie'nt to obtain a substantial increase'in the hardnes of thealloy.

4. A hard nickel-iron alloy containing about 2% to about 50% nickel, more than 1% to about 10% of titanium, and iron constituting substan- 2 tially the balance of the alloy, said alloy Ibeing age hardened by heating for a suflicient period of time and at a sufliciently high temperature between 750 C. and the melting point to dissolve at least a portion of the titanium in'the alloy, 2 cooling the alloy to a temperature below 750 C. and heating the alloy 'for a' suilicient period of time and at a sufliciently high-temperature below 750 C. to obtain a substantial increase in the hardness of the alloy. w

5. A hard nickel-iron alloy containing about 2% to about 50% nickel, more than 1% to about 4% of titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating for a suflicient period of time and at a sufficiently high temperature between 750 C. and the melting point to dissolve at least a portion of the titanium in the alloy, cooling the alloy to a temperature below 750 C. and heating the alloy for a suificient period of 40 time and at a sufliciently high temperature below 750 C. to obtain a substantial increase in the hardness of the alloy.

6. A hard nickel-ironalloy containing about 2% to about 50% nickel, about 2.2% to about 3.2% of titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating for a suflicient period of time and at a sufiiciently high temperature at least a portion of the titanium in the alloy, cooling the alloy to a temperature below 750 C. and heating the alloy for a suificient period of time and at a sufliciently high temperature below, 750 C. to obtain a substantial increase in the hardness of. the alloy.

7. A hard nickel-iron alloy containing about 2% to about 50% nickel, more than 1% to about 10% titanium, and iron constituting substantially the balance of the alloy, said alloy being age (:0 hardened by heating for a suificient period of, time at a sufficiently high temperature between 750 C. and the melting point of the alloy to cause at least a portion of the titanium to dissolvein the alloy, and cooling the alloy from the as aforesaid temperature to about 500 C. at a rate suinciently slow to cause a substantial increase thebalance of the alloy, said alloy beingv age hardened by heatingfor a suilicient period of time at 'a sufllciently high temperature between.

750 c. and the-melting point of'the alloy to 75 9. A hard nickel-iron alloy containing about 2% to about 50% nickel, about 2.2% to about 3.2% titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened byheating for a suflicient period of time at a sufliciently high temperature between 750 C. and the melting point of the alloy to cause at least a portion of the titanium to dissolve in the alloy, and cooling the alloy from the aforesaid temperature to about 500 C. at a rate sufficiently slow to cause a substantial increase in the hardness of the alloy.

10. A hard nickel-iron alloy containing about 20% to about 50% nickel, more than 1 to about 10% titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating the alloy to an elevated temperature below its melting point but sufficiently high to cause titanium to go into solution, quenching the alloy and reheating to a. temperature below that of the initial heating but sufliciently high and for a period oftime suflicient to obtain a substantial increase in the hardness of the alloy.

11. A hard nickel-iron alloy containing about 20% to about 50% nickel, more than 1 to about 4% titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating the alloy to an elevated temperature below its melting point but sufficiently high to cause titanium to go into solution, quenching the alloy and reheating to a temperature below that of the initial heating but sufliciently high and for a period of time sufficient to obtain a substantial increase in the hardness of the alloy.

12. A hard nickel-iron. alloy containing about 20% to about 50% nickel, about 2.2% to about 3.2 titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating the alloy to an elevated temperature below its melting point but sufficiently high to cause ,titanium to go into solution, quenching the alloy and reheating to a temperature below that of the initial heating but sufliciently high and for a period of time sufiicient to obtain a substantial increase in the hardness of the alloy.

13$ A hard nickel-iron alloy containing about 20% to about 50% nickel, more than 1% to about 10% of titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating for a sufiicient period of time and at a sufficiently high temperature between 750 C. and the melting point to dissolve at least a portion of the titanium in the alloy, cooling the alloy to a temperature below 750 C. and heating the alloy for a sufficient period of time and at a suificiently high temperature below 750 C. toobtain a substantial increase in the hardness of the alloy.

14. A hard nickel-iron alloy containing about 20% to about 50% nickel, more than 1% to about 4% of titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating for a sufficient period of time and at a sufficiently high temperature between 750 C. and the melting point to dissolve at least a portion of the titanium in the alloy, cooling the alloy to a temperature below 750 C. and heating the alloy for a suflicient period of time and at a sufliciently high temperature below 750 C. to obtain a substantial increase in the hardness of the alloy.

15. A hard nickel-iron alloy containing about 20% to about 50% nickel, about 2.2% to about 3.2% of titanium, and iron constituting substantiallythe balance of the alloy, said alloy being age hardened by heating for a sufficient period of time and at a sufllciently high temperature between 750 C. and the melting point to dissolve at least a portion of the titanium in the alloy, cooling the alloy to a temperature below 750 C. and heating the alloy for a sufiicient period of time and at a sufiiciently high temperature below 750 C. to obtain a substantial increase in the hardness of the alloy.

16. A hard nickel-iron alloy containing about 20% to about 50% nickel, morethan 1% to about 10% titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating for a suflicient period of time at a sufliciently high temperature between 750 C. and the melting point of the alloy to cause at least a portion of the titanium to dissolve in the alloy, and cooling the alloy from the aforesaid temperature to about 500 C. at a'rate sufliciently slow to cause a substantial increase in the hardness of the alloy.

17. A hard nickel-iron alloy containing about 20% to about 50% nickel, more than 1% to about 4% titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating for a suflicient period of time at a sufliciently high temperature between 750 C. and the melting point of the alloy to cause at least a portion of the titanium to dissolve in the alloy, and cooling the alloy from the aforesaid temperature to about 500 C. at a rate sufficiently slow to cause a substantial increase in the hardness of the alloy.

18. A hard nickel-iron alloy containing about 20% to about 50% nickel, about 2.2% to about 3.2% titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating for a sufiicient period of time at a suiliciently high temperature between 750 C. and the melting point of the alloy to cause at least a portion of the titanium to dissolve in the alloy, and cooling the alloy from the aforesaid temperature to about 500 C. at a rate sufiiciently slow to cause a substantial increase in the hardness of the alloy.

19. A hard nickel-iron alloy containing about 10% to about nickel, more than 1% to about 10% of titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating the alloy to an elevated temperature below its melting point but sufficiently high to cause titanium to go into solution, quenching the alloy and reheating to a temperature below that of the initial heating but sufficiently high and for a period of time sufiicient to obtain a substantial increase in the hardness of the alloy.

20. A hard nickel-iron alloy containing about 10% to about 50% nickel, more than 1% to about 10% of titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating for a suflicient period of time and at a sufficiently high temperature between 750 C. and the melting point to dissolve at least a portion of the titanium in the alloy, cooling the alloy to a temperature below 750 C. and heating the alloy for a suflicient period of time and at a sufllciently high temperature below 750 0. to obtain a substantial increase in the hardness of the alloy.

v 21. A hard nickel-iron alloy containing about 10% to about 50% nickel, more than 1% to about 10% titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating for a sufllcient period oi time at a suiliciently high temperature between 750 C. and the melting point of the alioy to cause at least a portion of the titanium to dissolve in the alloy, and cooling the alloy irom the aforesaid temperature to about 500 C. at a rate sufliciently slow to cause a substantial in- I time and at a suiliciently high temperature becrease in the hardness of the alloy.

' 22. A hard nickel-iron alloy containing about 10% to about 50% nickel. more than 1 to about 4% titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating the alloy to an elevated temperature below its melting point but ,sufliciently high to cause titanium to go into solution, quenching the alloy and reheating to a temperature below that of the initial'heating but sumcientiy high and for a period of time suflicient to obtain a substantial increase in the hardness of the alloy.

23. A hard nickel-iron alloy containing about 10% to about 50% nickel, more than 1% to about 4% of titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating for a suillcient period of I ness thereof.

tween 750 C. and the melting point to dissolve at least a portion of the titanium in the'alloy, cooling the alloy to a temperature below 750 C. and heating the alloy for a suflicient period of time andat a sufllciently high temperature below 750 C. to obtain a substantial increase in the hardness of the alloy.

24. A hard nickel-iron alloy containing about 10% to about 50% nickel, more than 1% to about 4% titanium, and iron constituting substantially the balance of the alloy, said alloy being age hardened by heating for a suflicient period of time at a sufliciently high temperature between 750 C. and the melting point oi the alloy to cause at least a portion of the titanium to dissolve in the alloy, and cooling the alloy from the aforesaid temperature to about 500 C. at a rate sui'iirciently slow to cause a substantial increase in the hardness of the alloy.

25. The process of producing a hard alloy composed of from 3 to 6 percent of titanium, a small amount of nickel, and the balance substantially all iron, which consists in the steps of heating the alloy to an elevated temperature below its melting point but sufiiciently high to cause the titanium to go into solution with the iron, quenching the alloy and reheating it to a temperature below that of the initial heating but sufliciently high and for a period of time sumcient to obtain a substantial increase in the hard- NORMAN B. PILLING. -PAUL DYER MERICA.- 

